We measured the IQ demodulation board gains for REFL11 and AS55.

To do this, we replaced the PD input on the demod board with an RF signal at near the nominal frequencies of 11.066195 MHz and 55.330975 MHz using a Marconi 2024A identical to the one which sources the PM sidebands in our PSL. Even though we matched the modulation frequencies we found the two marconis were in practice offset by ~ 3 Hz. After tuning the frequency around a bit, we managed to get them to within 450 mHz.

REFL11

We started with REFL11 IQ demod board. After sourcing 11.066198 MHz into the PD input port, we took the I and Q outputs and looked at them using an osciloscope. We measured the Vpp levels on both as well as the Marconi output. The resulting levels were

• Source = 44.4 mVpp, I = 8.8 mVpp and Q = 10.8 mVpp ==> Gains are therefore 0.19 and 0.24. The amplitude gain of this board is sqrt(0.19 ** 2 + 0.24 ** 2) = 0.153. This is in stark disagreement with the wiki. Has the wiki finally failed us?

AS55

We then moved on to AS55 IQ demod board. After sourcing 55.330975 MHz* into the PD input port, we took the I and Q outputs and looked at them using an osciloscope. We measured the Vpp levels on both as well as the Marconi output. The resulting levels were

• Source = 16.8 mVpp, I = 50.8 mVpp and Q = 56.3 mVpp ==> Gains are therefore estimated to be 3.3 and 3.7. The amplitude gain of this board is sqrt(3.3**2 + 3.7**2) = 4.74. This is in slight contrast with the previously measured gain of 2.8, but we think a factor of 2 may have been misplaced in either calculation since one typically estimates AMP = 2 * sqrt(I**2 + Q**2).

* Note that in the second test, we didn't match up the frequency, which caused I and Q outputs to have significant gains (instead of just I).

{Mayank, Paco, Yehonathan}

Dewhitening noise curves were taken using SR785+SR560 for the PRMI noise budget. One representative channel was measured at each board, suspensions were tripped before work was done. The input pins to the dewhitening boards were shorted using an exposed ribbon cable.

At each board, the measurement was taken with and without dewhitening filter on. The toggling of the dewhitening filter was done by turning on and off the SimDW filters at the coil filter screen of each suspension.

Attachment 1 summarizes the results.

ITMX dewhitening noise is much higher than the rest.

ITMY measurement turned out to be bogus since we mostly measured dark noise. The reason we made the gain so low in that measurement is that it was saturating the SR560 whenever we used gain>1.

I modified the analysis to correct for any affects due to Anti-Aliasing or Anti-Imaging filters, and I also found a insignificant error on how I was undoing the suppression due to MICH loop in the MICH data. I also propagated the calibration in MICH method better. Attached are the updated results. The upward swing is still present.

Also, last night, Koji and I looked into any frequency dependent deviation in sensing arm length between POY11 and BEATY_PHASE (using DFD+Phase tracker) This was done by locked the YARM to the main laser and locking YAUX to the YARM, sending excitationa at C1:SUS-ETMY_POSCAL_EXC and taking transfer function between C1:LSC-YARM_IN1 and C1:ALS-BEAT_Y_FINE_PHASE_OUT. This transfer function was flat upto about 600 Hz and the deviation from there to 2000 Hz was expected based on limited bandwidth of the phase tracker. I don't have the plot to attach, someone should redo this quick measurement to save the data.
Interestingly, the same measurement when done with  C1:LSC-DARM_IN1 in FPMI configuration did not show a flat response. This is can mean that the DARM strain relationship with the beatnote frequency deviation is not a simple constant factor and/or depends on DARM or CARM OLTFs. I leave my remarks on this project here for the baton to be picked up by others in future. I unfortunately only have this much time to contribute to FPMI calibration.

It has happened multiple times today that IMC has tripped on its own. Yehonathan and I have had to come back to manually lock IMC multiple times.

Wed Apr 26 10:24:07 2023 [EDIT]

[Paco] I aligned the MC by hand, let it run locked for 30 minutes without angular controls, and then switched on the WFS loops yesterday at ~ 6 PM. IMC has been locked ever since.

Yuta and I had a discussion last week about the signal strength between the configurations. Here are some naive calculations.
=== Please check the result with a more precise simulation ===

Michelson: Homodyne (HD) phase signal @44MHz is obtained from the combination of LO11xAS55 and LO CAxAS44. SBs at AS rely on the Schnupp asymmetry, the signal is weaker than the one with a single bounce beam from an ITM.

PRMI Carrier resonant:
- Despite the non-resonant condition of the sidebands, the HD phase signal @44MHz is expected to be significantly stronger (~x300) compared with the MI due to the resonance of the carrier and the 44MHz sidebands (the 2nd-order SBs of 11 and 55) in the PRC. Thus, the LO CAxAS44 term dominates the signal.
- The MICH signal @55MHz is enhanced by the resonant carrier by a factor of ~5.5, in spite of the non-resonant 55MHz SBs.
- The MICH signal @BHD is enhanced by the resonant carrier by a factor of ~300. This is the comparable phase sensitivity to PRFPMI case.

PRMI Sideband resonant:
- Despite the non-resonant condition of the carrier, the HD phase signal @44MHz is expected to be even stronger (~x400) compared with the MI due to the resonance of the 11MHz and 55MHz sidebands in the PRC. Thus, the LO11xAS55 term dominates the signal.
- The level of the MICH signal @55MHz is expected to be comparable to the one with PRMI carrier resonant as the resonant condition for the CA and 55MHz SBs are interchanged.
- The MICH signal @BHD is expected to be negligibly small due to non-resonance of the carrier.

PRFPMI: Now the carrier and the 11 and 55MHz sidebands are resonant.
- The HD phase signal @44MHz is expected to be the same level as the SB resonant PRMI, and the LO11xAS55 term dominates the signal.
- The level of the MICH sensitivity @AS 55MHz shows x300 of the MICH signal of the MI and x50 of the MICH with PRMI.
- The MICH signal @BHD is going to be the same level as the one with PRMI Carrier resonant.
- The DARM signal shows up at the dark port signal enhanced by x300 from the MICH level due to the finesse of the arms.

Simple assumptions
1) PRM has a transmission of T_PRM = 0.05
2) PRG is limited by the transmission of PR2 (T_PR2=0.02 per bounce).
    If the IFO is lossless, PRG is 25 (i.e. theoretical maximum). In reality, the IFO loss is 2~3% -> PRG is ~15.
    The asymmetry of 30mm has a negligible effect.
3) For the anti-resonant fields, APRG is ~T_PRM/4 = 0.0125
4) Arm finesse is 450. Therefore the phase enhancement factor N is ~300.
5) Modulation depth is ~0.1. J0=1, J1=0.05, J2=0.00125
6) Sideband leakage by the asymmetry is ɑ=l_asym wm / c = 0.008 for 11MHz and 5ɑ for 55MHz.

Single Bounce

The numbers are power transmission to each port
   Carrier              11MHz                    55MHz
LO TPRM TPR2 = 1.0e-3   J1^2 TPRM TPR2 = 2.5e-6  J1^2 TPRM TPR2 = 2.5e-6
AS TPRM/4    = 1.3e-2   J1^2 TPRM/4    = 3.1e-5  J1^2 TPRM/4    = 3.1e-5

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-6 * 3.1e-5) = 8.8e-6

Michelson

   Carrier               11MHz                     55MHz                      44MHz
LO TPRM TPR2 = 1.0e-3    J1^2 TPRM TPR2 = 2.5e-6   J1^2 TPRM TPR2   = 2.5e-6
AS TPRM ε^2  = 0.05 ε^2  ɑ^2 J1^2 TPRM  = 8.0e-9   25 ɑ^2 J1^2 TPRM = 2.0e-7  16 ɑ^2 J1^4 TPRM = 3.2e-10

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-6 * 2.0e-7)  = 7.1e-7
                 LO CA x AS 44 = Sqrt(1.0e-3 * 3.2e-10) = 5.7e-7

AS MICH  @55MHz: AS CA x AS 55 = Sqrt(0.05 * 2.0e-7) ε  = 1.0e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(1.0e-3 * 0.05) ε  = 7.1e-3 ε

PRMI (Carrier Resonant)

   Carrier              11MHz                     55MHz                      44MHz
LO PRG TPR2 = 0.3       J1^2 APRG TPR2 = 2.5e-7   J1^2 APRG TPR2   = 2.5e-7  J1^4 PRG TPR2 = 1.9e-6
AS PRG ε^2  = 15 ε^2    ɑ^2 J1^2 APRG  = 8.0e-10  25 ɑ^2 J1^2 APRG = 2.0e-8  16 ɑ^2 J1^4 PRG = 9.6e-8

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-7 * 2.0e-8)  = 7.1e-8
                 LO CA x AS 44 = Sqrt(0.3 * 9.6e-8)     = 1.7e-4
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(15 * 2.0e-8) ε    = 5.5e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(0.3 * 15) ε       = 2.1 ε
 

PRMI (Sideband Resonant)

   Carrier               11MHz                     55MHz                      44MHz
LO APRG TPR2 = 1e-4      J1^2 PRG TPR2 = 7.5e-4    J1^2 PRG TPR2   = 7.5e-4  J1^4 APRG TPR2 = 6.3e-10
AS APRG ε^2  = 5e-3 ε^2  ɑ^2 J1^2 PRG  = 2.4e-6    25 ɑ^2 J1^2 PRG = 6.0e-5  16 ɑ^2 J1^4 APRG = 3.2e-11

LO phase @44MHz: LO 11 x AS 55 = Sqrt(7.5e-4 * 6.0e-5)  = 2.1e-4
                 LO CA x AS 44 = Sqrt(1e-4 * 3.2e-11)   = 5.7e-8
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(5e-3 * 6.0e-5) ε  = 5.5e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(1e-4 * 5e-3) ε    = 7.1e-4 ε

PRFPMI

   Carrier             11MHz                     55MHz                      44MHz
LO PRG TPR2 = 0.3      J1^2 PRG TPR2 = 7.5e-4    J1^2 PRG TPR2   = 7.5e-4   J1^4 APRG TPR2 = 6.3e-10
AS PRG ε^2  = 15 ε^2   ɑ^2 J1^2 PRG  = 2.4e-6    25 ɑ^2 J1^2 PRG = 6.0e-5   16 ɑ^2 J1^4 APRG = 3.2e-11

LO phase @44MHz: LO 11 x AS 55 = Sqrt(7.5e-4 * 6.0e-5)  = 2.1e-4
                 LO CA x AS 44 = Sqrt(0.3 * 3.2e-11)    = 3.1e-6
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(15 * 6.0e-5) ε    = 3.0e-2 ε  ==> DARM@55MHz 9.0 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(0.3 * 15) ε       = 2.1 ε     ==> DARM@BHD   6.3e2 ε

Mayank and I worked on finalizing the plots for the beam offset from the dithering test done in 17552. Plotted in attachment 1 are the beamspot demodulated signals from MC_F_DQ which are averaged over 1 second each (blue) for YAW and PIT in MC1,2,3. The yellow line over each plot shows the 3 Hz lowpassed signal of the beamspot movement.

Additionally, we have seen no direct correlation to the WFS1 or 2 sensors due to the MC movements. This may be because the WFS display a complete signal that includes all changes in the cavity length due to the shaking of the mirrors. Thus, the signal (shown in red) of the WFS sensors will show a combined average of movement from all 3 dither lines.

This morning I found a helpful post in the git.ligo pages that referred to the issue that was stopping the summary pages from being submitted to the codor. In the last 3 weeks the accounting_tag ligo.dev.o3 was retired, and thus the accounting tag "ligo.dev.o3.detchar.daily.summary" which is found in both /condor/gw_daily_summary.sub and /condor/gw_daily_summary_rerun.sub was preventing the summary pages from bieng submitted.

The post referred to a running list in the nodus that points to all active accounting tags: etc/condor/accounting/valid_tags this showed that "ligo.dev.o4.detchar.daily.summary" and "ligo.dev.o5.detchar.daily.summary" were currently active tags. I then tested the files using this tag (o4) with success in starting the pages up again. I have now committed the change to the git. 

The prior 3 days of summary pages were also regenerated: 

relocate to /bin

run ./gw_daily_summary_40m --day YYYYMMDD

once finished run ./pushnodus YYYYMMDD

      (must do independently for each day)

this afternoon I did some swapping around of linear and RL for IMC WFS.

In the end, I left in in the 'both' state:

• The WFS1,2,MC_TRANS PIT loops are all on but with -40, -40, -20 dB of nominal gain
• the RL is on for PIT

this is so that we have good DC control with integrators and good HF performance too.

Last night I took ITMY calibration data using MICH with AS55_Q. Adding that to the same plot. The error bars are probably underestimate with the MICH calibration method due to systematics not taken into account. For this measurement, MICH was locked with low UGF of 20 Hz to avoid all lines in MICH loop. Notches at the line frequencies were also put in. MICH OLTF was measured and any possible suppression of lines has been compensated for (very small). Note that error bars are present for DFD method too, but they are too small in this scale.

MICH calibration did not independently verify the higher actuation strength found by DFD methods at higher frequencies. For an ideal pendulum, the calibration constants should ahve been freqeuncy independent. It does see higher calibration constant values at 500 Hz and 1.4 kHz lines, but with a lot of noise. See attachment 2 for the calibration in real time, but this plot is bit messy. For the three lower frequency lines, DFD+Phase tracker and DFD with offline analysis match in their estimates , there is a significant mismatch at 500 kHz line and we do not have data for doing this for 1.4 kHz line.

I did offline analysis with the available data. We were only saving signals at 2048 Hz rate, so analysis can not be done on 1.4 kHz line. See attached plot for the difference in the two analysis.

We are aiming to prepare a realtime system deployable calibration method, that's why we were using phase tracker. Note that the calibration results with phase tracker have been compensated for any lack of gain due to phase tracke limited bandwidth, open loop gain of aux loop or remaining suppression from YARM loop despite the notches.

About the moku, we think that something is wrong in connection of moku output to ADC. We see the same cal line heights in the moku app in ipad but after going through ADC, we see about 10 times less line heights and 10 time sles noise floor too. But when we stick a marconi split between DFD and moku, we see the same results, so we are not sure what is wrong with it but it is not trustworthy. Maybe the order of magnitude noise reduciton is because of this factor of 10 that happens when it reads beatnote. To be solved in future, we will carry on with DFD for now.

how about the other idea of downloading the I & Q channels and doing the analysis offline? I'm curious if its better or worse. How could the Moku possibly be better?

Another idea is to use the frequency divider and then directly digitize. I believe someone tried that a few years ago, but not sure how good it was.

[Anchal, Paco]

We updated the LSC model to use the amplitude as a normalization (analogous to what happens in OpLevs). For reference Attachment #1 shows the previous model detail, and Attachment #2 shows the updated one. We then built, restarted and ran the model to realize the phase tracker gain can now be set once and for all assuming we still have a simple integrator and 2 kHz of phase tracker bandwidth. Doing this results in the ALS residual noise shown in Attachment #3. Compared against the reference spectra, the improvement is modest but not as great as what the moku had.

We ran ITMY actuation calibration using this infrastructure; to do this we lock arm cavities to PSL, lock AUX lasers to arm cavities, turn on our five lines and read back the demodulated signals from the beatnote as it goes through DFD + phase tracker. The results are summarized in Attachment #4. This time we correctly accounted for all known sources of statistical and systematic uncertainties (including a recently  measurement of the AUX loop gain),

Today, we ran dither lines on the MC1,2,3 mirrors in YAW from 136598007 to 1365981967 and similarly on PIT from 1365982917 to 1365984618.

The following frequencies and amplitudes were recorded for each dither line:

The urad conversions used to calculate theta DC and AC can be found at 17481

The dither lines were then demodulated in python and the steps shown in 17516 were followed to calculate the beam offset that each dither line represented in pitch and yaw. 

The following results were found:

Attatched bellow is the power spectrums for both yaw and pitch.

[Yehonathan, Paco]

Repeated the coil dewhitening check for BS. Attachment #1 show results. Note however the DW filter shape for BS is more complicated:

Note that YAW data here is actually PIT data and PIT data is plotted twice, as we messed up with data saving...

 

Repeated also for ITMX. See Attachment #2.

[Mayank, Paco, Yohanathan, Yuta]

We checked if coil dewhitening switch is working by measuring transfer function from coil outputs to oplev pitch and yaw.

Method:
 - Turned off oplev damping loops (this actually changed the result, this means that oplev loops have quite high UGFs)
 - Measured transfer functions from C1:SUS-PRM_(UL,UR,LR,LL)COIL_EXC to C1:SUS-PRM_OL_(PIT|YAW)_OUT, with SimDW and InvDW filters on/off.
 - Injected excitations are about 30000 at 100 Hz and 3000 at 10 Hz.
 - When SimDW and InvDW filters are on, analog dewhitening filter should be off, so it should give suspension mechanical response and other filter shapes in coil driver.
 - When SimDW and InvDW filters are off, analog dewhitening filter should be on, so it should give the same transfer function with analong dewhitening filter.
 - Taking the ratio between two should give analog dewhitening filter shape, which is zero at [70.7+i*70.7,70.7-i*70.7] Hz and pole at [10.61+i*10.61,10.61-i*10.61] Hz, from SimDW filter.

Notebook: /opt/rtcds/caltech/c1/Git/40m/measurements/SUS/PRM/CoilDewhitening/PRMCoilDewhiteningCheck_COIL2OL.ipynb

Result:
 - Attachment #1 shows the result for each coil. 4th panel is the ratio, which should match with analog dewhitening filter shape.
 - The result looks consistent with our expected analog dewhitening filter shape.

Next:
 - Repeat this measurement for other suspensions.
 - PRM suspension response have residual frequency dependence from 1/f^2. What is this?

First, simple stuff. We estimate the noise budget with total input and output noises. Later, we will break it down (ADC, DAC, whitening, dewhitening noises etc.):

We take the dark noise of AS55, REFL11 and make sure that the whitening and "unwhitening" software filters are on (attachment 1)

To convert cts to Watts we use the values from previous MICH noise budgeting for AS55:

PD_responsivity = 1e3*0.8 #V/W
ADC_TF = 3276.8 #cts/V
demod_gain = 2 #6.77 #According to https://wiki-40m.ligo.caltech.edu/Electronics/LSC_demoddulators
whitening_gain = 10**(24/20) #24 dB

We are not sure why the demod gain was chosen to be 2 and not 6.77 as in the Wiki, maybe it was chosen to match the measurements back then. The demod gain for AS55 was actually measured to be 2.4 in elog 16961.

For now, for lack of time, we use the PD responsivity and demod gain of REFL11 from the wiki:

PD_responsivity = 4.08e3*0.8 #V/W
ADC_TF = 3276.8 #cts/V
demod_gain = 4.74 #According to https://wiki-40m.ligo.caltech.edu/Electronics/LSC_demoddulators
whitening_gain = 10**(18/20) #18 dB

Using the Finesse model for PRMI (should push to git) we calculate the sensing matrix (attachment 3). We turn off the HOMs as it gives us strange results for now.

We take the output noise that was measured at the output of the BS coil driver measured in elog 16960.

Attachment 2 shows the estimated PRMI noise budget. Notice that the dark noise contribution is an order of magnitude better than MICH (elog 16984) due to PRG.

Attached are the Rayleigh spectrograms of the error/control signal channels associated with the NN nonlinear control of IMC (pitch). The 4-hour data stretch starts at 3:45pm PDT on 4/18. The spectrograms were generated with (stride=5, fftlength=2, overlap=1). PNG images are attached for reference; the generated pdf files were too large to include here or send over email.

The Rayleigh statistic measures nongaussianity of the data.

[Anchal, Yuta]

We have repeated LO phase noise measurement done in elog 40m/17511.
Method we took was the same, but this time, we used (1+G)*[C1:HPC-LO_PHASE_IN1]/[optical gain] to estimate the free-running noise, instead of using [C1:HPC-LO_PHASE_OUT] multiplied by LO1 actuator gain.
We confirmed that both method agrees down to ~ 10 Hz (at lower frequencies, OLTF measurement is not robust; we used interpolated measured OLTF (Attachment #1) for compensation).
Below is the summary of optical gains etc measured today.
Filter gains were adjusted to have UGF of 50 Hz for all.

LO_PHASE lock in ITMX single bounce
        Demod phase  Optical gain     filter gain
BH55_Q  -102.7 deg    6.9e9 counts/m  -0.34
BH44_Q  -5.7 deg     1.3e10 counts/m  -0.17

LO_PHASE lock in MICH
        Demod phase  Optical gain     filter gain
BH55_Q  -72.6 deg    8.7e8 counts/m   -4.4
BH44_Q  -27.6 deg    8.8e8 counts/m   -2.2

LO_PHASE lock in FPMI
        Demod phase  Optical gain     filter gain
BH55_Q  24.2 deg     3.7e9 counts/m   -0.67
BH44_Q  2 deg        5.3e8 counts/m   -4.4  (An order of magnitude smaller than elog 40m/17511)

The values are consistent with elog 40m/17511, except for BH44 in FPMI.
It took sometime to robustly rock LO_PHASE with BH44_Q in FPMI today.
After some alignment, offset tuning and demod phase tuning, it finally worked.
Demod phase of BH44 was tuned to have more DC signal when LO_PHASE was locked with BH55_Q, considering that BH55 and BH44 are orthogonal.
It actually created BH44_I having more amplitude (some noise?) than BH44_Q, but BH44_Q was more coherent to LO_PHASE fringe in BH55_Q.
It might be related to why we are not dark noise limited for BH44_Q, while BH55_Q is dark noise limited in FPMI, and why we cannot lock FPMI BHD with BH44.

Anchal and I turned on another RL policy (ninedwarfs) with Chris's help.

It looks to be performing great, with good low frequency suppression and low noise injection at higher frequencies.

Going to leave it on overnight. It seems to respond well to lockloss of IMC, me whacking the MC2 chamber, walking near the MC2 chamber, kicking the optics by step in actuators, and turning off the sensors for a few seconds. Pretty robust!

I was able to get this accelerometer going for the next Lab tours. I want to get this guy up on a big screen to give people a nice "wow". I found this accelerometer on the Y end cabinet and there is 1 more available if anyone needs it at 40m. It is a Brüel & Kjær 8318. It contains a PZT so there is no need to input a signal. The accelerometer seemed to only put out roughly 2 mV max, so i had to amplify with an SR560 to get a good looking signal. 

RXA: link to Manual

Ditto of 40m/17543 but for XBEAT >> Calibrated to 0.3061 +/- 0.0001

An interesting thing to look at is the ALS out of loop spectra using our Moku DPLL. Attachment #1 shows the calibrated noise spectra in Hz/rtHz of both XBEAT and YBEAT as taken by the Moku phasemeter when the ARM cavities are locked to PSL using POX/POY. A great improvement is noted at lower frequencies (almost an order of magnitude for Y, over an order of magnitude for X) and some residual seismic noise (between ARMs and IMC) is noticeable! At higher frequencies, the suppressed laser frequency noises are close to their former references.

However this is only great news for our ALS calibration scheme, as the DPLL range is limited and may not be useful for the usual CARM offset reduction using ALS.

The rms fluctutations for the ALS beatnotes using the Moku Phasemeter have dropped below the 100 Hz floor! We now have 50-55 Hz (before we had 200 to 300 Hz)

Took some ITM/ETM single arm calibration data using Moku Phasemeter ALS>

• ITM gpstimes = [1365471104 to 1365471582]
• ETM gpstimes = [1365472286 to 1365473448]

I then took some ITM actuation calibration data using the Michelson fringe. For this I lock MICH and turn on all five lines using AS55_Q >

• ITMX gpstimes = [1365474355 to 1365474788]
• ITMY gpstimes = [1365474816 to 1365475268]
• Free swing = [1365475309 to 1365475535] (to get the fringe amplitude)

The ETM actuation calibration at these frequencies can be transferred using the POX/POY error signals and the ITM calibration from the gpstimes above. This should allow us a back to back cross-calibration comparison for arm cavities. Full analysis to follow this entry.

Finally, please take note of the area around the LSC rack! The temporary Moku phase meter calibration and setup referenced above are still a bit in the way. See Attachment #2

I calibrated the moku phasemeter setup for reading beatnote fluctuations today. The calibration is referred to the DFD output (not including the phase tracker) channels by using the measurement made by gautam in 40m/14981.

Measurement setup

• Set marconi to 40 MHz carrier, FM1 sine deviation of amplitude 2000 kHz (we expect maximum beatnote fluctuation of ~1.8 kHz for 50 pm length modulation in the arm length) at 145 Hz.
• The output of amrconi is splitted, one half going to DFD for BEATY, one half going to Moku Phasemeter input 1.
• Moku phase meter is set with following settings:
  • Input1:
    • Frequency : Auto
    • Bandwidth: 1 MHz
    • Coupling: AC
    • Impedance: 50 Ohms
    • Range: 400 mVpp
  • Output1:
    • Signal Freq offset
    • Scaling: 1 mV/Hz
    • Invert: Off
    • Offset: 0
    • Range: 10 Vpp
• Measurement taken from 1365442502 to 1365444003

Analysis

• Read channels C1:ALS-BEATY_FINE_I_OUT C1:ALS-BEATY_FINE_Q_OUT C1:ALS-BEATY_MOKU_PHASE_IN1 for 500s.
• Used np.arctan2(Q, I) to read DFD phase output. Multiplied it by 1e6/70.973 to convert it into Hz using DFd calibration by Gautam in 40m/14981. This measurement brings in 340 ppm of uncertainty in the measurement.
• Demodulated the phase at 145 Hz to get the signal sent by Marconi. Blue trace in the attachment is this signal.
• Demodulated Moku phase output at 145 Hz and calculated the calibration constant required to match the ampltiude with 400second averaged DFD output.
  Calibration constant came out to be: 0.2953 +/- 0.0001
• Multiplied the calibration constant to moku phase output. This is the orange curve in the attachment.
• With this method, we get 0.035% uncertainty on phase calibration from Moku.
• We can now use moku phasemeter for calibration measurements as the pahse tracker gain is not high enough for calibration lines above 200 Hz.

[Paco, Yuta]

We measured the power around BHD PDs to see if the numbers make sense.
Measured values are 10-20% less than expected values, which sounds good.
BHD DC PDs require slight reduction of gains to avoid saturation.

What we measured and result:
 - We measured the power with a Newport power meter (Model 840) for BHD A and B right after the viewport (A path and B path), in front of BHDC A and B, and in front of BH44 and BH55.
 - Note that BH44 is a pick-off from A path and BH55 is a pick-off from B path (see Attachment #1). A path also has a pick-off to BHD camera. So the measured numbers roughly sum up.
 - Measurement was done with LO beam only (misaligned AS4) and PRM misaligned, and PRMI carrier locked (forgot to misalign AS beam, but the most of the power is from LO beam).
 - Results are the following.

        LO beam only        PRMI carrier locked
        (PRM misalgined)    
A path  450 +/- 10 uW       110 +/- 10  mW
B path  360 +/- 10 uW       91 +/- 5 mW
BHDC A  330 +/- 10 uW       74 +/- 1 mW
BHDC B  320 +/- 10 uW       74 +/- 4 mW
BH44    100 +/- 3 uW        27 +/- 2 mW
BH55    3 +/- 1 uW          10 +/- 2 mW

                    LO beam only        PRMI carrier locked
                    (PRM misalgined)
C1:HPC-BHDC_A_OUT16 104                 saturated at ~22000
C1:HPC-BHDC_B_OUT16 103                 saturated at ~22000

Consistency check with previous measurement:
 - Power with LO beam only was measured in July 2022 (elog 40m/17046).
 - Compared with values in July 2022, it is now 10-20% less. This could be explainable by PMC transmission power drop on Dec 27, 2022 by ~10% (elog 40m/17390).

Expected values:
 - Expected values using PSL output of 890 mW (measured in elog 40m/17390) and calculated PRG of 13.4 (elog 40m/17532) are the following (see, also elog 40m/17040). Note that BHD BS has the transmission of 44% and the reflectivity is 56%.

A path, LO beam only
 890 mW * 0.9 (IMC transmission?) * 5.637%(PRM) * 2.2%(PR2) * 56%(BHDBS) = 560 uW
B path, LO beam only
 890 mW * 0.9 (IMC transmission?) * 5.637%(PRM) * 2.2%(PR2) * 44%(BHDBS) = 440 uW
A path, PRMI carrier locked
 890 mW * 0.9 (IMC transmission?) * 13.4(PRG) * 2.2%(PR2) * 56%(BHDBS) = 130 mW
B path, PRMI carrier locked
 890 mW * 0.9 (IMC transmission?) * 13.4(PRG) * 2.2%(PR2) * 44%(BHDBS) = 100 mW

  - Measured values are 10-20% less than expected values.

BHDC PD saturation:
 - Expected counts for C1:HPC-BHDC_A_OUT16 when PRMI carrier locked using LO beam only numbers are

 104 / 5.637% * 13.4 = ~25000

 - So, we are barely saturating.

Next:
 - Measure PRG using POPDC.
 - Reduce transimpedance gain of BHDC A and B by small amount to avoid saturation.

[Yuta, Radhika]

We copied the coil balancing procedure found in /scripts/SUS/coilStrengthBalancing/AS1/CoilStrengthBalancing.ipynb to a new PRM directory. After modifying channel names for PRM, we followed the coil balancing procedure:

1. Locked PRY. This was chosen since full PRCL lock was not maintainable for the duration of measurement.

2. Injected 13 Hz line into the butterfly mode and looked for a peak in the LSC PRCL control signal (C1:LSC-PRCL_OUT_DQ). It appeared like the existing coil gains for PRM are already tuned to minimize the but-pos coupling.

3. Injected 13 Hz line into the POS mode and looked for a peak in the PRM oplev pitch and yaw signals (C1:SUS-PRM_OL_PIT_IN1_DQ / C1:SUS-PRM_OL_YAW_IN1_DQ). Like above, the existing coil gains seemed to be tuned to minimize the pos-angle coupling.

The attached spectrum was taken when POS was excited at 13 Hz using LOCKIN1. As expected the PRCL control signal sees the actuation, but we do not see a 13 Hz peak in the oplev pitch/yaw signals.

I measured the OLTF of the XAUX-PDH loop [Attachment 1] now that the green laser is stably locking. I injected an excitation (100mVpp) at the error point of the loop using a Moku:Go. The excitation was summed with the PDH error signal (alpha) using an SR560, and the summed signal (beta) was sent to the PDH servo. (The Moku excitation was buffered with another SR560.) The transfer function beta/alpha was measured on the Moku. 

The loop has a UGF of 26.3 kHz, and a phase margin of ~25º (using 1/1-OLG convention).

Next steps:

- Replace PDH servo demod + controller with Moku:Go lock-in amplifier (ensure loop shape is maintained)

- Deploy digital filters to further increase loop bandwidth/phase margin

[Paco, Radhika]

To determine the PRM angle-to-length coupling for PRCL, we want to inject pitch/yaw lines into PRM and find the corresponding peaks in the PRCL closed-loop control signal (below loop UGF). Below is a summary of PRMI locking efforts.

Locking PRMI carrier

- Locked arm cavities, ran YARM, XARM ASS to get PR2/PR3 alignment

- Locked MICH to dark fringe

- Aligned PRM by maximizing drop in REFLDC (reaches 2 when well aligned)

         *This was the hurdle when attempting to lock PRMI last week*

- Locked PRMI carrier using configurations in PRMI-AS55_REFL11.yml. There is now a "Lock PRMI (carr) using AS55/REFL11" action on the LSC screen that runs operateLSC.py with the aforementioned yaml file.

- Final DoF gains used: MICH --> 0.8; PRCL --> -0.07. At times BS was being kicked too hard, so we reduced the MICH gain from 1.2.

Lock stability

During PRMI lock, REFLDC was noisy with ~1 Hz fluctuations. We got PRMI to stay locked for a couple minutes at a time. Additionally it couldn't lock the AS port to dark fringe, and it stayed bright while tweaking the BS alignment.

We took spectra of ASDC during a lock stretch to quantify the DC power fluctuations at the AS port [Attachment 1]. The red trace is ASDC with PRMI locked. REF0 (black) is ASDC with MICH locked; REF1/REF2 (blue/green) are ASDC with single-bounce PRCL locked (either ITMX or ITMY misaligned). Note that the PRMI spectrum might need to be normalized by the PRCL gain / PRM transmission: ~ 10/0.057 = 175. The factor difference in ASDC fluctuations between MICH and PRMI for a single test point is ~144 --> with PRMI normalized, the ASDC fluctionations are comparable with MICH.

I'm going to get into the PSL enclosure. Also turn on the HEPA for a while during the intrusion.
Work done.

Start of the work:
(cds) ~>gpstime 
PDT: 2023-04-06 21:09:36.670623 PDT
UTC: 2023-04-07 04:09:36.670623 UTC
GPS: 1364875794.670623

End of the work:
(cds) ~>gpstime 
PDT: 2023-04-06 21:19:37.331716 PDT
UTC: 2023-04-07 04:19:37.331716 UTC
GPS: 1364876395.331716

I've turned on NN controller for MC WFS PIT loops. One can disable this controller and go back to linear controller by sitemap>IOO>C1IOO_WFS_MASTER>Actions!>Stop Shimmer . One can start the controller again sitemap>IOO>C1IOO_WFS_MASTER>Actions!>Run Shimmer .

[Paco, Radhika]

We calibrated the PRM oplev.

We took calibrated spectra of oplev PIT and YAW (Attachment 1) with the oplev loops open and closed. We see noise suppression up until a few Hz, as expected. The high-frequency floor appears to be at 1e-9 rad/rtHz with this calibration.

Next steps: improving PRMI angular control

I ran two recently trained neural network controllers today between 10 am and Noon. Each test comprised of four segments:

• All loops open
• Linear loop closed
• Neural Network working alone
• Neural Network + Linear Loop

The latest controller unfortunately failed in both cases, working alone and working together with linear loop.

The second latest controller functioned well, keeping the arm locked throughout.

<p>I purchased some more of these from DigiKey. These parts are currently in the EE shop. These are replacements for the NDP5565 part of the SR560.</p>

[Paco, Radhika]

We locked PRMI in carrier.

We refereced the old IFOconfigure script (/opt/rtcds/caltech/c1/burt/c1ifoconfigure/C1configurePRM_Carr.sh) to manually configure the LSC screen for PRMI. The final MICH/PRCL gain values used to achieve lock were flipped in sign:

(.snap file ---> final value)

The FM trigger levels (enable/disable) for PRCL and MICH were set to (150/50). The following filter modules were engaged:

During PRMI lock, the POPDC level reached 13130 counts, or 6.8 mW (using calibration of 1.931e6 counts/W). The POPDC counts level was ~1330 with only MICH locked, meaning the PRC gain was ~10. Attachment 1 is an image of REFL, AS, and POP monitors during lock.

Lock was maintained for close to a minute, allowing us to estimate the UGF at around 100 Hz. We used the AA_PRCL_UGF_meas.xml template to measure the loop transfer function. The GPS time (start, end) for a lock stretch with boost on is (1680547905, 1680547933 1364583160, 1364583442).

Next steps

1. Achieve better angular alignment to keep MICH locked to dark fringe - ASS? Seismic FF?

Here are our best estimates for the optic transmission (power) coefficients.

Assuming our input power to the IFO is 0.95 Watts, and the IMC transmission is 90%, about 855 mW should be incident on the PRM. Furthermore, following our recent estimates we can estimate our PRMI gain to be ~ 13.4.

• Using these numbers we expect a single pass AS power of 517.8 uW and LO power of 530.1 uW when the PRM is misaligned and MICH is free swinging, consistent with recent estimates. When the PRM is aligned we would then expect the max PRMI BHD single port flash to be 7.6 mW.
• Similarly, using these numbers we expect a single pass POPDC power of 1.01 mW, which then is expected to flash at a ~ 13.5 mW level when the PRM is aligned. The POP beam is split between the position sensor, our broadband POP22 and POP110 RFPD, and a CCD camera to monitor the POP beam.

POPDC calibration

I misaligned the PRM and ITMX to get a single ITMY bounce configuration. From the numbers above, I should expect a single ITMY bounce POPDC power of 255 uW. Instead, I measure a total of 173.5 uW = 78 uW (POP QPD) + 91 uW (POP RFPD) + 4.5 uW (POP camera) which is 50% less than expected .  The C1:LSC-POPDC_OUT level for this measurement was 335 counts, giving a rough empirical calibration of 1.931e6 counts / W. When the PRM is aligned and the MICH is free swinging, the POPDC flashes reach levels in excess of 14,500 counts implying 7.51 mW PRMI POPDC power. When PRM is misaligned the POP MICH flashes reach 1360 counts, implying 703 uW (which falls short by ~ 50% from our expectation).

There is probably an unaccounted BS in the ITMX table that may explain our observed difference. Nevertheless, our POPDC calibration should be good from here on.

After the XAUX - XARM lock was recovered the C1:ALS-TRX_GAIN was set from 0.002 to 0.0006 to normalize the green transmission to 1 when the cavity is aligned. This situation was verified with YAUX as well. The green transmissions are now normalized to 1 when both arm cavities are aligned.

After this I took a reference ALS noise spectra (Attachment #1). The XALS rms noise is ~ 100 Hz (which is great compared to previous reference of > 250 Hz), while the YALS is slightly worse at high frequency but the rms is comparable to previous references (~ 250 Hz). This is somewhat encouraging for our future PRFPMI lock acquistions.

Stable lock of the X End green laser was recovered.

- The biggest issue was that the laser PZT input had been terminated with a 50ohm at the laser head. (See Attachment 1: The terminator has already been removed in the photo.) Since the PZT output of the servo box (output impedance 10Ohm) goes through 680Ohm at the summing node for the modulation, the PZT output was attenuated by a factor of 15. This made the required servo gain for locking more than the box could deliver. More importantly, the PZT range (in terms of the laser frequency) was also limited. Momentary locks were still possible with the reduced range and gain. However, the actuation signal hit the rail within a few seconds because of the pendulum motion.

Once the terminator was removed from the head, the Xarm was locked with the green laser like a charm.

- On the way to the resolution, I had to go through the full scrutinization of the loop components one by one. Here is the record of the findings:

• Inspected the green Refl PD (Thorlabs PFA36A). The gain setting of the PD was 40 dB, and the unlocked output voltage was 10.8 V. This is not only very close to saturation, but also the bandwidth drops below the modulation frequency (150 kHz according to Thorlabs' manual). The gain was changed to 20dB. This made the unlocked PD output to be 1.08V and the BW was expected to be 1MHz.
   
• Checked the LO setting. The box has a label saying "LO 7dBm". The function generator setting of "0.66 Vrms" resulted in 7.0dBm at the mixer LO input. So this number is used. Exactly the same amount goes to the PZT summing node.
   
• Checked the mod freq. The PDH error signal amplitude was maximized at 278.5kHz (mixer output observed with 50Ohm: 46.0mV), however, the signal looked distorted from the text-book shape of the PDF error. This means that the demod phase was not optimized.
  The mod freq of 287.5kHz made the PDH error signal look better while the response was weaker (mixer out: 31.2mV). It turned out that the cavity locking didn't like these mod freq between 280kHz~290kHz. The momentary lock stretches showed a lot of quasi-sinusoidal fluctuation ~600Hz in the error and transmission signals. Instead, the modulation of 210.5kHz was used. This made the error signal during lock stretches clean and tight. 
   
• Box inspection: Checked the signal ratio between the error in and the error mon. The monitor gain seemed x20~x21. The PZT output and the PZT mon had identical gains. The transfer function of the box was measured with the gain knob changed from 0.00 to 7.00 where the transfer function started to get distorted with the given input. The gain was increased by 5dB/turn (i.e., 1 turn increases the gain by 5dB). ? It does not match with the info on the schematic and the datasheet? Anyways, the gain knob is working fine.
   
• To resurrect the SLOW THERMAL servo, the monitor channels were connected to the DAQ interface. The existing slow channel servo/setting worked fine, wh
   
• Usual caution: a slight touch to the satellite amp caused the UR OSEM PD completely black out. It means that just your presence at the X end can make some changes to the suspension.
   

I confirmed that MC Length feedback path to MC2 position is present and has been turned off in recent history. Feedback filter module can be seen in sitemap>IOO>Lock MC>MC2_LSC where the bottom fitler module is for feeding back MC Length to MC2. See attached screenshot.

This feedback signal goes and gets added to MC2 suspension longitudnal signal through ALTPOS path which is nominally not shown in any of the suspension screens (including the old ones). Note that this path is different than the LSC path that comes into each suspension screen.

Today, I tried a quick turning ON of this apth without playing around with any of the filters to see if the feedback helps. On first glance, it does not seem to help. Probably the gain values and filter modules need ot be adjusted. See attachment 2.

I'm turning this off again and in future someone should take a look at this loop.

I repeated the calculations but with FPMI (last case was all MICH). The qualitative behavior is the same, the BH55 sensing is mostly affected by residual darm offset. If the darm offset is of a couple of nm, the single RF sideband may sense the LO phase at as much as > 20 deg away from the nominal phase angle. This is not too different from the MICH case; so maybe I overlooked something about how I define FPMI in the calculation.

Attachments #1-3 show the plots of the BH55 (single RF sideband) and BH44 (double RF sideband) sensitivity to LO phase fluctuations around various nominal LO phase angles. Attachment #1 looks at the effect of differential loss, Attachment #2 looks at the effect of differential dc reflectivity (of the ITMs), and Attachment #3 looks at the effect of residual darm offsets. Dashed lines show the orthogonal quadrature (I) of the demodulated RF signals (always minimized).

I've updated c1ioo model with adding WFS sensor to optic angle matrix and output filter module option. The output filter modules are named like EST_MC1_PIT to signify that that these are "estimated" angles of the optic. We can change this naming convention if we don't like it. I've also started DQ on the outputs of these filter moduels at 512 Hz sampling rate.

No medm screens have been made for these changes yet. One can still access them through:

For SENS_TO_OPT_P Matrix

For SENS_TO_OPT_Y Matrix

For filter modules:

but what about including the DC reflectivity imbalance of the arms? there would be another BH55 term from that field maybe.

Yuta pointed out that the BH55 signal was weirdly never going to zero, so I actually tuned the demod angle and made sure I was reading the right (Q) quadrature. This doesn't affect our previous qualitative conclusion about DARM offsets, but here's an updated gif which also makes visualization easier (?).

that is really a lot of high precision for the REFL_11 demod phase...

for this kind of measurement, I wish we had a python code that would plot this measurment relative to our Finesse/PyKat model so we know if this table is like "Oh, nothing to see here." or "Wow! that's a Nobel prize worthy measurement !!"

PRMI sensing matrix was measured under PRMI locked with REFL55_I and Q.
MICH actuator is 0.5*ITMX-0.5*ITMY (to have more pure MICH, according to 40m/15996) and PRCL actuator is PRM.
RF demod phases seem to be good within a degree or so to minimize PRCL component in Q.

Sensing matrix with the following demodulation phases (counts/m)
{'AS55': 2.1, 'REFL55': 76.02, 'REFL11': 32.63833493469488}
Sensors       MICH @311.1 Hz           PRCL @313.31 Hz           
AS55_I       (+0.31+/-1.48)e+09 [90]    (+6.56+/-2.23)e+10 [0]    
AS55_Q       (-3.49+/-0.87)e+08 [90]    (+4.62+/-1.80)e+09 [0]    
REFL55_I       (-1.52+/-5.61)e+09 [90]    (+3.21+/-1.36)e+11 [0]    
REFL55_Q       (+8.77+/-0.46)e+09 [90]    (+5.01+/-3.63)e+09 [0]    
REFL11_I       (-0.23+/-1.92)e+08 [90]    (+1.13+/-0.47)e+10 [0]    
REFL11_Q       (+0.39+/-2.14)e+07 [90]    (-4.00+/-9.79)e+07 [0]    

Phase for AS55 to minimize PRCL in Q is 6.14+/-2.08 deg (4.04+/-2.08 deg from current value)
Phase for REFL55 to minimize PRCL in Q is 76.91+/-0.75 deg (0.89+/-0.75 deg from current value)
Phase for REFL11 to minimize PRCL in Q is 32.44+/-0.50 deg (-0.20+/-0.50 deg from current value)

Next:
 - Lock PRMI in carrier
 - PRG is not so stable; Measure g-factor of PRC using Kakeru-Gupta method (40m/8235)

PRM actuator was calibrated using PRY by comparing the actuation ratio between ITMY.
It was measured to be

PRM : -20.10e-9 /f^2 m/counts

This is consistent with what we have measured in 2013! (40m/8255)

Method:
 - Locked PRY using REFL55_I using the configuration described in 40m/17521 (UGF of ~100 Hz)
 - Measured transfer function from C1:LSC-(ITMY|PRM)_EXC to C1:LSC-PRCL_IN1
 - Took the ratio between ITMY actuation and PRM actuation to calculate PRM actuation, as ITMY actuation is known to be 4.90e-9 /f^2 m/counts (40m/17285).

Result:
 - Attachment #1 is the measured TF, and Attachment #2 is the actuator ratio PRM/ITMY.
 - The ratio was -4.10 on average in 70-150 Hz region, and PRM actuation was estimated to be 4.90e-9 * -4.10 /f^2 m/counts.

MICH actuator for PRMI lock:
 - When BS moves in POS by 1, BS-ITMX length stays the same, but BS-ITMY length changes by sqrt(2), so MICH changes by sqrt(2) and PRCL changes by -sqrt(2)/2.
 - So PRM needs to be used to compensate for this, and the ratio will be BS + k * PRM, where

 k = 26.54e-9/sqrt(2) / -20.10e-9 * sqrt(2)/2 = -0.66

 - So, good MICH actuator will be 0.5 * BS - 0.33 * PRM, which is not quite consistent with the rough number we had yesterday (-0.275; 40m/17521), but agrees with the Gautam number (-0.34; 40m/15996).
 - PRMI sensing matrix for REFL55 needs to be checked again.

Summary of actuation calibration so far:
 They are all actuator efficiency from C1:LSC-{$OPTIC}_EXC

BS   : 26.54e-9 /f^2 m/counts in MICH (40m/17285)
ITMX :  4.93e-9 /f^2 m/counts (40m/17285)
ITMY :  4.90e-9 /f^2 m/counts (40m/17285)
LO1  : 26.34e-9 /f^2 m/counts (40m/17285)
LO2  :  9.81e-9 /f^2 m/counts (40m/17285)
AS1  : 23.35e-9 /f^2 m/counts (40m/17285)
AS4  : 24.07e-9 /f^2 m/counts (40m/17285)
ETMX : 10.91e-9 /f^2 m/counts (40m/16977, 40m/17014)
ETMY : 10.91e-9 /f^2 m/counts (40m/16977)
MC2 : -14.17e-9 /f^2 m/counts in arm length (40m/16978)
MC2 :   5.06e-9 /f^2 m/counts in IMC length (40m/16978)
MC2 :  1.06e+05 /f^2 Hz/counts in IR laser frequency (40m/16978)
PRM : -20.10e-9 /f^2 m/counts (40m/17522)

[Paco, Yuta]

We locked PRMI in sideband using REFL55_I and REFL55_Q.
Lock is not quite stable probably due to alignment fluctuations, and power recylicing gain is breathing.

PRMI preparations:
 - We aligned PRM using PRY (PRM-ITMY) cavity. Aligning PRM to oplev QPD center or last PRM alignment values in May 2022 (! see 40m/16875) didn't work, but we were in the middle of these two, both in pitch and yaw.
 - After this, we centered PRM oplev, aligned REFL camera, POP RFPD (which provides POP22, POP110, and POPDC), and REFL11.

PRY/PRX locking:
 - PRY/X was locked using REFL55_I or REFL11_I. Locking configuration which gives UGF of ~100 Hz was as follows

REFL55_I (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-PRCL_GAIN=-0.03
REFL11_I (18 dB whitening gain, 32.55 deg demod angle) C1:LSC-PRCL_GAIN=-0.8
FM4,5 used for acquisition, FM1,2,6,9 turned on triggered.

 - Attachment #1 is the measured OLTF when PRY was locked.
 - When PRY is flashing, ASDC_OUT, POPDC_OUT, POP22_I, POP11_Q flashes upto 0.33, 1000, 30, 80, respectively.

PRMI locking:
 - PRMI was locked using REFL55_I for PRCL and REFL55_Q for MICH using the following configurations to give UGF of ~100 Hz for both DoF.

PRCL
  REFL55_I (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-PRCL_GAIN=-0.03
  FM4,5 for acquisition, FM1,2 turned on triggered using POPDC.
  Actuating on 1 * PRM

MICH
  REFL55_Q (24 dB whitening gain, 76.02 deg demod angle) C1:LSC-MICH_GAIN=+0.9
  FM4,5 for acquisition, FM1,2 turned on triggered using POPDC.
  Actuating on 0.5 * BS - 0.275 * PRM

 - REFL55 demodulation phase was the same as FPMI and PRY. We checked this is roughly enough by measuring the sensing matrix to minimize PRCL component in Q.
 - MICH actuation of PRM/BS ratio was roughly tuned by minimizing the sensing of MICH component in REFL55_I.
 - PRCL and MICH gain was estimated by measuring the amplitude of error signals in PRY or PRM-misalgined MICH, and comparing that in PRMI.
 - Attachment #2 shows the screenshot of the configuration.
 - Attachment #3 and #4 are measured OLTF for PRCL and MICH.
 - Attachment #5 shows the time series data when PRMI is locked.

Next:
 - Tune PRM local damping
 - Tune REFL55 demodulation phase better by measuring the sensing matrix
 - Measure PRM actuation efficiency to check what is the right BS/PRM balancing
 - Estimate power recycling gain and compare with expectations
 - Lock PRMI using REFL11, AS55
 - PRMI BHD

I drafted a calibrated LO Phase noise budget using diaggui whose template is saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/LO_PHASE_cal_nb.xml which includes new estimates for laser frequency and intensity noises at the LO phase when MICH is locked (whether they couple through MICH or the LO path is to be determined with noise coupling measurements in the near future, but we expect them to couple through the LO phat mostly).

Attachment #1 shows the result.

Laser Frequency Noise

To calibrate the laser frequency noise contribution, I used the LO PHASE error point away from the control bandwidth (~ 20 Hz) and the calibrated C1:IOO-MC_F control point (in Hz) which should represent the laser frequency noise above 100 Hz. and dithered MC2 at frequencies around to 130, 215, and 325 Hz to match the LO phase error point with the MC_F signal. I was expecting to use a single 0 Hz pole + gain (to get the phase equivalent of the laser frequency noise) but in the end I managed to calibrate with a single gain of 3.6e-7 rad/Hz and no pole. Since the way the laser frequency noise couples into our BHD readout may be complicated (especially when using BH55 RF sensor) I didn't think much of this for now.

Laser Intensity Noise

For the intensity noise, I followed more or less a similar prescription as for laser frequency noise. This time, I used the AOM in the PSL table to actuate on the 0th order intensity going into the interferometer. Attachments #2-3 show the connection made to the RF driver where I added a 50 mVpp sine (at an offset of 0.1 V) excitation in the AM port to inject intensity noise calibration lines at 215 and 325 Hz and matched the LO_PHASE error point with the BHDC_SUM noise spectrum.

I have changed the MC SUS output matrices by a few % for some A2L decoupling - if it causes trouble, please feel free to revert.

Anchal came to me and said, "I think those beam offsets are a bunch of stinkin malarkey!", so I decided to investigate.

Instead of Alex's "method" of trusting the actuator calibration, I resolved to have less systematics by adjusting the SUS output matrices ot minimize the A2L and then see what's what vis a vis geometry.

The attached screenshot shows you the measurement setup:

1. copy the DoF vector from DoF column into the LOCKIN1 column.
2. Turn on the OSC/LOCKIN for the optics / DoF in question (in this example its MC2 PITCH)
3. Monitor the peak in the MC_F spectrum
4. Also monitor the mag and phase of the TF of MC_F/LOCKIN_LO
5. use the script stepOutMat.py to step the matrix

Next I'm going to modify the script so that it can handle input arguments for optic/ DOF, etc.

FYI, the LOCKIN screens do have a TRAMP field, but its not on the screens for some reason . Also the screens don't have the optic name on them. :

SUS>caput C1:SUS-MC2_LOCKIN1_OSC_TRAMP 3
Old : C1:SUS-MC2_LOCKIN1_OSC_TRAMP   0
New : C1:SUS-MC2_LOCKIN1_OSC_TRAMP   3

After finishing the tuning of all 3 IMC optics, I have discovered that 27.5 Hz is a bad frequency to tune at: the Mc1/MC3 dewhtiening filters have a 28 Hz cutoff, so they all have slightly different phase shifts at 27-28 Hz due to the different poles due to tolerances in the capacitors (probably).

*Also, I am not able to get a real zero coupling through this method. There always is an orthogonal phase component that can't be cancelled by adjusting gains. On MC3, this is really bad and I don't know why.
 

This is interesting. With the FPMI, the DARM phase shift is enhanced by the cavity. Therefore, I suppose the effect on the BH55 is also going to be enhanced (i.e. a much smaller displacement offset causes a similar LO phase rotation).

[Paco, Yehonathan]

I took over the finesse calculations Yehonathan had set up for BHD. The notebook is here and for this post I focused on simulating what we might expect from our single RF vs dual RF sensors (55 MHz and 44 MHz respectively) in terms of LO phase control.

The configuration is simple, only MICH is included (no ETMs, no PRC, no SRC). The LO phase is changed by scanning LO1, the differential loss is changed by scanning the ITMXHR loss parameter (nominally at 25 ppm), and the microscopic DARM offset is changed by scanning the BS position by +- 6 nm.

Finesse estimates the sensor response by taking the demodulated sideband magnitude (BH55, BH44) with respect to a 1 Hz LO1 signal modulation. This can be done for a set of LO phase angles so as to get the nominal LO phase angle where the response is maximized.

I first replicated the plots from [elog17170] for the two sensors in question. This is just done as a sanity check and is shown in Attachment #1. This plot summarizes our expectation that the single RF sideband sensor should have a peak response to the LO phase around 90 deg away from the nominal BHD readout phase angle (0 deg in this plot). In contrast, the double RF demodulation scheme has a peak response around the nominal LO phase angle.

Attachment #2 looks at a family of similar plots representing differential loss changes between the two MICH arms. We tune this by changing the ITMX loss in finesse, and then repeat the calculation as described above. It seems that for the simple MICH, differential loss of ~ 10000 ppm does not impact the nominal LO phase angle where the responses are maximized for either sensor (note however that the response magnitude maybe changes for single RF sideband sensing at extremely high differential loss).

Finally, and most interestingly Attachment #3 looks at a family of similar plots representing a set of microscopic DARM offsets (+- 6 nm). This is tuned by changing the BS position ever so slightly, and the same calculation is repeated. In this case, the nominal LO phase angle does change, and it changes quite a lot for the single RF demod. It looks like this might be enough to explain how we can sense the LO phase angle with a single RF sideband, but I think the next interesting point would be to simulate the effect of contrast defect by changing the ITM RoCs (to scatter into HOMs) or the non-thermal ITM lenses (to probe the TEM00 contrast defect effect). Any comments / feedback at this point are welcome, as we move forward into other configurations where more serious thermal effects might be introduced (PRMI).

I have organized the resulting data from running dither lines on MC1,2,3. The data has been collected from diaggui as shown in attachment 1.

Mirror		Avg Re (+/- 1000)	Avg Im (+/- 1000)	Peak Power ()	Cts/urad
MC1	21.12	7000	4000	8062	12.66
MC2	25.52	13000	10000	16401	6.83
MC3	27.27	4000	-600	4044	11.03

Next using the following equations we can find :

Where is the change in length in result of the dithering and is the overall change in beam spot position

Delta L can be calculated by:

where is the peak power of the line frequency and is found by taking the square root of the magnitude of the Real and imaginary terms, is frequency the laser light is traveling at (281 THz) and is the lenght of the IMC (13.5 meters).

can then be calculated by:

where  is the angle at which the mirror was shaken at a given frequency. We can find  by converting the amplitude of the frequency that the mirror was shaken at and converting it into radians using the conversion constants found here: 17481.

is then shown to be found by this angle diveded by the line frequency.

The final values are calculated and displayed bellow:

Mirror
MC1	157.9 urad	0.35 urad	0.38 nm	1.08 mm
MC2	146.4 urad	0.23 urad	0.78 nm	3.39 mm
MC3	226.7 urad	0.31 urad	0.19 nm	0.61 mm

With Anchal's help, I have setup dither lines for Rana on MC1,2,3 that will be running overnight. The oscilations were set on MC1,2,3, oscillator screens.
The following table describes the current setup:

These frequencies and amplitudes were set on LOCKIN1 for each MC1,2,3. The output filters matrix for MC1,2,3 was also updated to reflect the degree of freedom being tested: PITCH.

The frequencies were picked to avoid the dewhitening frequency: 28Hz, and the Bounce/Roll frequencies: 16 Hz & 24 Hz. Furthermore, decimal value frequencies were utilized to avoid the multiples of 1 Hz.

The oscilators were originally started at 1363480200 and will be turned off at 1363535157.

See attachment 1 for the plot of the power spectrum. This test is done to find the beam offset for pitch.